Field of the Invention
The present invention relates to an imaging lens which forms an image of an object on a solid-state image sensor such as a CCD sensor or C-MOS sensor used in a compact image pickup device, and more particularly to an imaging lens which is built in an image pickup device mounted in an increasingly compact and low-profile smartphone, mobile phone, PDA (Personal Digital Assistant), game console, information terminal such as a PC or robot, home appliance or vehicle with a camera function.
Description of the Related Art
In recent years, there has been a general tendency that many information terminals have a camera function. Also, various products with high convenience such as home appliances with a camera have been introduced into the market. The demand for home appliances and information terminals which have a camera function is expected to grow and efforts to develop such products will be accelerated.
The imaging lenses mounted in such products are strongly anticipated not only to provide high resolution to cope with an increase in the number of pixels but also to be compact and low-profile enough to match the trend toward a more compact and low-profile product and offer high brightness and a wide field of view.
One approach to meeting this demand may be to increase the number of constituent lenses from five to six, in order to obtain a higher resolution, since an imaging lens composed of six constituent lenses is higher in design freedom and more advantageous in correction of various aberrations than an imaging lens composed of five constituent lenses.
However, when the imaging lens is composed of six constituent lenses, the larger number of constituent lenses may lead to a longer total track length. Also, in order to provide an imaging lens which meets all the demands for low-profileness, a wide field of view and a low F-value, the problem of difficulty in correction of aberrations in the peripheral area of an image must be addressed. Unless the problem is addressed, it is difficult to deliver high optical performance throughout the image.
In the conventional art, for example, the imaging lenses described in Patent Literature 1 (JP-A-2012-155223) and Patent Literature 2 (US 2012/0243108) are known as imaging lenses composed of six constituent lenses.
Patent Literature 1 discloses an imaging lens which includes, in order from an object side, a first lens group with positive refractive power, a second lens group with negative refractive power, a third lens group with positive refractive power, a fourth lens group with negative refractive power, a fifth lens group with positive refractive power, and a sixth lens group with negative refractive power.
Patent Literature 2 discloses an imaging lens which includes, in order from an object side, a first lens with positive refractive power having a convex surface on the object side, a second lens, a third lens, a fourth lens having at least one aspheric surface, a fifth lens having a convex surface on the object side and a concave surface on an image side, and a sixth biconcave lens having at least one aspheric surface.